Scientists have not yet proven cause and effect. But climate researcher Peter Stott says extreme weather events are on the rise — as climate models have long predicted

Peter Stott

From the brutal heat wave in Russia that may have killed 15,000 people, to the devastating floods in Pakistan that have displaced millions more, extreme weather events and the climatic processes that lead to them have been in the news all summer long.

But is it really quite so clear cut? To what degree is climate change leading to increases worldwide in extreme weather events?And what further research is needed in this area?

To get some answers, I interviewed Peter Stott for “How on Earth,” the weekly science and environment radio program on KGNU FM radio here in Boulder. Stott is head of climate monitoring and attribution at the United Kingdom’s Met Office. He is in Colorado this week for the first full session of a scientific group called the Attribution of Climate-related Events. ACE consists of scientists from the National Center for Atmospheric Research, the UK Met Office, and the National Oceanic and Atmospheric Administration.

Click here to listen to the interview at KGNU. (Scan forward to about 14 minutes and 20 seconds into the broadcast to access the beginning of the interview segment.)

And for excerpts and additional perspective on these issues, continue reading . . .

Despite the claims of bloggers and climate activists, Stott as well as other experts say that it is impossible to say that a particular extreme weather event like the Pakistani floods or the Russian heat wave were “caused” by global warming. They offer more nuanced, if still sobering, assessments.

From the interview:

I think . . . some people are too easily jumping from the very clear evidence that climate is changing, and that we’ve seen systematic changes in our climate system over the last few decades, to saying that particular individual extreme weather events are therefore due to climate change and therefore will become more frequent in the future . . .

The example with the current terrible situation in Pakistan is a very good case in point. Although our understanding of the climate system does tell us, and the observations do tell us, that there have been increases in extreme rainfall events, we don’t know about the particular circumstances in Pakistan, and the particular weather situation there, whether that is the sort of thing that will become more frequent or not. And, therefore, [we don't know how to] respond to such a situation in terms of the longer-term adaptation response, for example.

What we would like to do with further research is really nail down whether what we’re looking at has more to do with variability of the climate system — are we seeing a very rare meteorological event? . . . which may not be the sort of thing that becomes more common in the future — or whether we are seeing something that really is the sort of thing that a particular locality can expect to see more of in the future.

I pointed out that recent analyses from both NASA and NOAA pegged January through July as the hottest such period on record. Seventeen countries had record temperatures this summer. And in addition to the floods, Pakistan had Asia’s hottest day ever recorded. In May, one city reached 53.5 degrees Celsius, which is 128 degrees Fahrenheit. On the other hand, such extremes are a natural part of the climate system. “So as a scientist, what can you say with fair confidence now about this summer’s events?,” I asked Stott.

To start off with, you highlighted the global temperature. And that’s right, globally temperatures are very warm, historically. We’ve shown . . . that the first decade of the 21st century was the warmest decade on record. And that is very clear.

Alongside this global warming has come some some very consistent consequences that climate models have long predicted . . . including the fact that the atmosphere has gotten more humid, and including the fact that there are broad scale changes in the precipitation patterns over the surface of the Earth. And also alongside with that has come a clear trend that’s been observed in the number of extreme temperatures that have been measured, and also the fact that there have been more heavy rainfall events.

So all of this adds up to a consistent picture. And it really means that the chances that we’ve got it wrong, that the scientific consensus is wrong about that this, that there isn’t a major human influence on climate — the chances that that’s the case seems to keep reducing as we get more and more data.

In other words, it is true that what we saw this summer fits the pattern of observed increases in certain kinds of extreme weather events. Moreover, these increases are consistent with our understanding of the physics of climate change. And they have long been predicted by computer models.

But cause and effect is something else. The whole point of the ACE workshop that Stott is attending is to figure out how scientists can do a better job of attributing the specific causes of these events.

We’re interested in being able to respond better to the question that always gets asked when we have extreme weather events . . . which is, what has caused them both meteorologically and whether they are linked to climate change or not.

This is scientifically both an important area and also I think a relatively new area . . . Although there has been a lot of work done on the very large scale global climate changes, in terms of the temperatures and the very large scale rainfall patterns . . . there has been relatively little work done looking much more closely at whether particular extreme events, whether they be the floods in Pakistan or heat waves in Russia or even the very cold winters that parts of the U.S. and the U.K. have had recently — whether these are linked to just natural variability . . . or whether these are the sorts of the things that we would expect more of in the future because of climate change.

In a recent New York Times article, Gavin Schmidt, a climate scientist with NASA, summed up the issue succinctly: “If you ask me as a person, do I think the Russian heat wave has to do with climate change, the answer is yes. If you ask me as a scientist whether I have proved it, the answer is no — at least not yet.”

Great catch, Tom. If at all possible I think it would be good to get a posty-conference interview with one of the other participants.

Here’s my take on the problem:

Formal attribution is a model-based exercise that presents a very, very high bar for individual events, since it basically requires a proof that such an event is impossible in the absence of anthropogenic influences. One can speak of likelihoods rather than certainty, but the basic problem remains.

IMHO tobacco represents an ideal analogy. For example, what does a doctor say to a patient who asks if their lung cancer was a consequence of smoking? Even though not all lung cancers of smokers are caused by smoking, since among other things we know that non-smokers get lung cancer while not all smokers do, the doctor is going to answer something like “very likely” or even just “yes.”

Similarly, cigarette packs now contain rather simple phrases like “smoking causes cancer” even though its application to the individual buying the pack is less than certain.

I picked this off the Surgeon General’s site:

Advise all tobacco users to quit. Use clear, strong, and personalized language. For example:

“Quitting tobacco is the most important thing you can do to protect your health.”

Thanks Steve for your comments. I think they add a helpful dimension to the discussion of this issue.

Whether climate scientists should use the same approach as the Surgeon General is really a critical question. For what it’s worth, here are my two cents as a science writer (who might be accused of being too close to his cautious sources!):

The problem with dropping the nuance and simply saying that global warming “causes” extreme weather events is that while many people will accept it, many others will doubt it — because they know at least intuitively that the climate system is incredibly complex and that cause and effect is a very difficult thing to prove. For these folks, dropping the nuance may simply undermine credibility.

I actually think we don’t give people enough credit for being able to understand issues like this in terms of probability. (That was one lesson I learned from Stephen Schneider.) And I think they can very well understand what Kevin Trenberth has been saying. In essence: The answer to the question, “Does global warming cause heat waves and floods” is that “it’s not so simple.”

In an interview with the Christian Science Monitor, here’s how he actually worded it:

Basically, I think Trenberth, Schmidt, Stott and Schneider got it right: We don’t need to treat global warming like cigarettes — we don’t have to label it with, “CAUTION: THE IPCC HAS DETERMINED THAT GLOBAL WARMING CAUSES EXTREME EVENTS LIKE HEAT WAVES AND FLOODS.” Most people are smart enough to understand that environmental science usually paints more in shades of gray, not black and white. And also that when you put together enough dark gray pixels, the appearance is pretty darn close to black.

One question that arises is at what point can we logically say that global warming is driving events? Even if we shift to a mid-Piacenzian-like climate state it would be hard to prove that most non-polar climate extremes are impossible with the current climate.

Also, are you familiar with John Sterman’s work? I think he’s solidly demonstrated that a very large chunk of the population doesn’t deserve the credit you want to give them. Interestingly this inability to understand the problem doesn’t seem to be correlated with intelligence.

Your headline, respectfully, is total and absolute nonsense. Climate models have never predicted any rise in extreme weather events anywhere. Anyone who suggests that they are even remotely capable of that is either ignorant or dishonest. Or perhaps you just being provocative because you knew that? Actually i don’t blame you because trenberth spouts this blatant untruth all the time. That warmer weather may affect weather extremes has to be proven via the statistical records – nothing to do with models -, and the longer term the better for the analysis. No such case has been made. Tou do get short term cherry picking I’ll grant you but a scince journalist should see through that one easily – well ok Revkin didn’t either.

Also a rise in extreme weather events was also predicted to happen by global cooling in the 70′s. Which is it then?

The worst part is the convenient short memory syndrome. During the cold Northern Winter when activists were exhorting us all to stop confusing weather and climate, my prediction was that there would be summer heatwaves and all these selfsame activists would be talking out of the other side of their mouths, and confuse weather and climate. I hereby further predict another cold Winter and another barrage of excuses for it – possibly involving global warming permanently altering the jet stream. We’ll see. So far my seasonal predictions are better than the Met Office. Admittedly not a difficult thing to achieve.

Paulina: There are simple quotation marks around the word “cause” — no “scare quotes.” The headline refers to a post at Climateprogress, which explicitly states that causation has been demonstrated. The word “cause” is used, so I quoted it.

Concerning your objection to the inherent logic of the headline:

A headline is a rhetorical device used to grab the attention of readers. It must be accurate and true to the story. But by definition, it cannot include all of the information that a reader needs for a full understanding of the story, or even its main point. Readers know that they will get a full explanation when they read the piece.

In this case, the headline is simply getting at this main point: “Based on their best understanding of the climate system right now, scientists cannot say that global warming caused the Russian heat wave and Pakistani floods.”

Obviously, all of that information cannot be included in a short, one-line headline. So the hed must be an abbreviation. The full logic of the main idea cannot be included.

I think most readers got the point when they read the story, which of course is the intention of every headline in the first place — to prompt readers to actually read the piece and thereby get the full story. But if you feel this headline is misleading and illogical, you’re entitled to your opinion. So far, no one else has complained.

Yulsman writes: “Stott as well as other experts say that it is impossible to say that a particular extreme weather event like the Pakistani floods or the Russian heat wave were “caused” by global warming.”

But Stott’s statements do not support Yulsman’s claim of impossibility, which is a remarkably strong — and not accurate — claim.

Demonstrating causation between the thermal forcing of greenhouse gases on the climate system and its particular state at a particular time and place (i.e. weather) may be difficult, problematic, or challenging, but it is not a priori “impossible.”

For example, a perfectly reasonable — and eminently practical — definition of causation is whether it can be shown that the existence of a particular prior factor makes an otherwise extremely unlikely result a highly likely result, particularly when coupled with a mechanistic understanding of how that factor could lead to that result.

Thus it is entirely reasonable to say that a worker’s exposure to asbestos caused his mesothelioma, an AIDS patient’s HIV caused his Kaposi sarcoma, someone’s lifetime of cigarette smoking and MacDonald’s burgers caused his heart attack.

It’s not “impossible” to say it. In fact, it’s the only reasonable thing to do.

Clearly, some people take vigorous exception with the headline and my statement that it is impossible to say that a particular extreme weather event like the Pakistani floods or the Russian heat wave was “caused” by global warming, So I am doing further reporting, which will form the basis either of an additional comment here or a new post. It may take me a few days. Whatever I learn I will share here.

Public attitudes about climate change reveal a contradiction. Surveys show most
Americans believe climate change poses serious risks but also that reductions in greenhouse gas (GHG) emissions sufficient to stabilize atmospheric GHG concentrations can be deferred until there is greater evidence that climate change is harmful. US policymakers likewise argue it is prudent to wait and see whether climate change will cause substantial economic harm before undertaking policies to reduce emissions. Such wait-and-see policies erroneously presume climate change can be reversed quickly should harm become evident, underestimating substantial delays in the climate’s response to anthropogenic forcing. We report experiments with highly educated adults – graduate students at MIT – showing widespread misunderstanding of the fundamental stock and flow relationships, including mass balance principles, that lead to long response delays. GHG emissions are now about twice the rate of GHG removal from the atmosphere. GHG concentrations will therefore continue to rise even if emissions fall, stabilizing only when emissions equal removal. In contrast, most subjects believe atmospheric GHG concentrations can be stabilized while emissions into the atmosphere continuously exceed the removal of GHGs from it. These beliefs – analogous to arguing a bathtub filled faster than it drains will never overflow – support wait-and-see policies but violate conservation of matter. Low public support for mitigation policies may arise from misconceptions of climate dynamics rather than high discount rates or uncertainty about the impact of climate change. Implications for education and communication between scientists and nonscientists (the public and policymakers) are discussed.

IMHO you were a bit quick to lump Trenberth, Schmidt, Stott, and Schneider together in support of the idea that Americans can be relied upon to bridge this conceptual gap based on the shades of grey inherent in the details of the science. The more I consider it, the more I think the tobacco analogy is perfect in every way: We need clear, simple messaging up front. That CSM article is actually a great example of how at present every scientist seems to have a different rhetorical approach. They need to get on the same page, and hopefully the conference will make some progress toward that goal.

“Based on their best understanding of the climate system right now, scientists cannot say that global warming caused the Russian heat wave and Pakistani floods.”

Obviously there’s a lot more to be said about all this, and I look forward to your follow-up post.

It struck me that one thing you might want to do is look closer at what Stott and others have to say about the difference in the state of knowledge about the heatwave and the flooding.

But, for now, let me push once again on the headline. Appreciating headline constraints, is the headline accurate and true to the point you are trying to make with it?

Suppose we don’t know enough “to say” that global warming caused the heatwave. Is “global warming did not “cause” the heatwave” an accurate headline, true to the point that we don’t know enough to say?

[...] Tom Yulsman has an interesting article based on an interview with Peter Stott. What struck me though was Steve Bloom’s comment, comparing the manner in which doctors talk about the health risks of smoking versus how climate scientists talk about the climatological risks of greenhouse gas emissions. See also this pointy comment by SecularAnimist. Doctors tend to be much more upfront about the risks than climate scientists are (see also my previous post). Possibly related posts: (automatically generated)Open letter of US NAS members on climate change and the integrity of scienceShould energy policy be linked to climate change?Just the facts, madam, just the facts won’t doA stormy future? [...]